The Goldman Sachs analysis says that the all-cash share of sales has more than doubled over the past seven years.

More than half of all homes sold last year and so far in 2013 have been financed without a mortgage, according to an analysis by economists at Goldman Sachs Group.

The analysis estimates that around 20% of all homes sold before the housing crash were “all-cash” sales (or around 30% of sales by dollar volume). But over the past seven years, the all-cash share of sales has more than doubled, increasing by more than 30 percentage points, according to economists Hui Shan, Marty Young and Charlie Himmelberg.

The Goldman study analyzed home sales figures from the Census Bureau and the National Association of Realtors and mortgage-origination data from the Mortgage Bankers Association and Lender Processing Services.

The surprisingly large cash-share of purchases helps to explain why home sales have jumped over the past two years despite more muted increases in broad measures of new mortgage activity, such as the MBA’s mortgage application index.

There’s no exact way to know who is responsible for all of these cash purchases, though they are likely to include some combination of investors, foreign buyers, and wealthy homeowners that don’t want to go through the hassle of getting a mortgage before closing on a sale. Mortgage lending standards have sharply tightened up since the housing bubble, with banks scrutinizing borrowers’ tax returns and bank statements to verify their incomes and the source of their down payment.

The Goldman analysis also estimates that around 44 cents of every $1 of homes sold currently is being financed, compared to 67 cents before the crisis.

Purchase-mortgage origination volumes have fallen from around $1.5 trillion in 2005, when the housing market peaked, to around $500 billion in each of the last two years.

While declines in the volume of homes being sold accounts for some of the decline, the Goldman economists estimate that around 40% of the decline is due to the drop-off in the amount of financing per home.

The Goldman analysis estimates that purchase-loan volumes will rise to around $750 billion next year and to $1.1 trillion by 2016.